Primary inductive charging devices are recent developments. The use of inductive charging is becoming more widespread, since, because there is no need for a specific connection interface, it enables wireless charging and can be adapted to many applications including, in particular, a “charging bench” surface which is used to simultaneously recharge a number of portable devices. Furthermore, it enables charging to be combined with a billing function for billing for the electrical power supplied. Inductive charging is becoming a universal charging standard.
Inductive charging makes use of the electrical phenomena of magnetic coupling between two windings, that of the primary device and that of the secondary device, which enables the electromagnetic transfer of voltage. An AC current in the winding of the primary device produces a variable magnetic field, the field lines of which transect the winding of the secondary device. This transection of the secondary winding by field lines of varying intensity induces a current in this winding. The voltage created by this current can then be used to power the secondary device or to charge its battery. The efficiency of the transfer depends on the quality of the coupling between the two windings.
Inductive charging requires a communication function that is specific to it, in order to control charging based on reception, by the primary device, of information relating to the charge level, the charging rate, or the bill for the power supplied. The primary device then processes the information in order to deduce therefrom possible actions to take: stopping of the charging, whether completely or temporarily, triggering of a billing process, etc.
Many ways of improving inductive charging have been provided recently, such as those published in patent documents U.S. 2010/0066305, U.S. 2011/0025265 or U.S. 2011/0285348.
Document U.S. 2010/0066305 in particular describes various operations that must be carried out in order to charge a secondary device, especially: placing the winding of the secondary device opposite that of the primary device; providing control and contactless communication functions in order to monitor charging of the secondary device; and stopping the charging once it is complete. One of the drawbacks of this type of device lies in the need to stop the charging in order to carry out the indispensible steps of communication and in order, in particular, to verify the charge level of the secondary device. The charging is interrupted so that the communication can be transmitted without interference or parasitic noise.
Document U.S. 2011/0025265 describes a primary device equipped, in addition to the winding provided for the electrical charging, with a second antenna for proximity wireless communication with the secondary device, and a secondary device also equipped with a second antenna. This second antenna is mainly dedicated to communication between the primary device and the secondary device. Nevertheless, during the communication phase, the charging is stopped, otherwise this charging interferes with the communication via harmonic noise. In addition, the constraint imposed on the secondary device, namely the use of a specific second antenna, deprives the wireless charger of its universal nature.
As for document U.S. 2011/0285348, it relates to improvements to the manufacture of the winding of the secondary device; it is formed by molding in one of the constituent layers of the secondary device. A winding molded in this way has two advantages: durability and thinness.
However, these devices do not enable, in good conditions, charging of the secondary device by the primary device simultaneously with communication between these two devices. Such simultaneity allows the charge level to be monitored in real time and the power emission to be decreased or stopped as soon as the secondary device signals that it is fully charged.
In these prior-art devices, the charging flux and the communication flux combine together as an amplitude modulation. The modulation index, which expresses the ratio of the amplitude of the information to the amplitude of the carrier, remains extremely small, about 1%, because the emitting antennas exhibit strong resonance, in order to increase their quality factor, and continuous emission. This small modulation index makes decoding the communication difficult and uncertain. In addition, the communication interferes with the charging flux, decreasing resonance between the two windings and therefore decreasing the efficiency of the transmission of energy between them.